1. Field of the Invention
The present invention relates to a roller width adjusting device for a divided type molding roller used in manufacturing a welded steel pipe.
2. Description of Related Art
One type of molding roller device used conventionally in a production line for continuously processing a strip into a welded pipe includes an upper roller and a lower roller. The strip is passed between the upper and lower rollers and bent in a so-called flower. However, with this type of molding roller device, each time the pipe size is changed, the molding rollers need to be changed. Therefore, it is necessary to have different size molding rollers. Moreover, changing these molding rollers is difficult and expensive.
Therefore, the recent trend is to use a divided type roller system. The divided type roller system comprises left and right divided molding rollers. An interval between the two rollers can be adjusted to change the size of the pipe that is to be produced. Examples of divided type roller systems and their associated adjusting means are discussed below.
A spiral type of adjusting means for a divided type roller system is disclosed in Japanese Patent Laid-Open Gazette No. Sho 57-28627. In particular, a molding roller comprising left and right divided rollers continuously molds a metallic strip into a desired shape. In this system, an outer shaft is fitted onto an inner shaft and both the shafts are connected to each other by keys. An internal screw thread in the divided rollers mates with an external screw thread on an outer periphery of the outer shaft. A nut rotatably mates with a groove in a side surface of the divided roller and is movable parallel to the axis of the outer shaft along a key way provided on the outer periphery of the outer shaft. An interval or distance between the divided rollers is adjusted by use of screw threads formed on the inner shaft and outer shaft. However, when the divided rollers are subjected to a large load, it is likely that the inner or outer shaft will break due to the concentration of stress on the screw threads. Furthermore, there is no backlash adjusting mechanism, which is necessary for manufacturing a pipe with a thin steel sheet because precise accuracy is needed.
In the Japanese Patent Laid-Open No. Sho 57-209722, an adjusting means is disclosed which changes the interval between divided rollers. In particular, a breakdown roller stand having an upper roller and a lower roller with an adjustable interval therebetween is used for manufacturing an electric seamed steel pipe. The upper roller and lower roller each include a pair of roller members. Between the pair of rollers is a removable spacer for setting the desired interval therebetween. A fixing means is provided for fixing the pair of roller members to each other at the desired interval. To change the divided rollers for a different size pipe requires the use of a different spacer interposed between the pair of left and right divided rollers. This requires considerable time and labor.
Furthermore, in the Japanese Patent Laid-Open Gazette No. Hei 3-138023,a roller hydraulic clamp system is used to adjust the positions of the divided rollers. In particular, left and right divided rollers are adjusted into different positions by use of threaded shafts. The divided rollers are fixed to the main shafts by use of a hydraulic clamp unit provided at the roller holders, respectively. A rotary joint is used as hydraulic supply means for the hydraulic clamp. However, with this device high speed manufacturing of pipe is difficult due to the limited life span of the oil seal. To avoid this, a cooling water distribution piping may be used to limit the heat exposure to the seal. However, this makes the roller rotation device complicated.